The present invention concerns a process for the production of pure lecithin, which is directly usable for physiological purposes, by extraction with supercritical gas.
The term lecithin designates a group of substances belonging to the series of phosphatides. These compounds, which contain the element phosphorus in the form of phosphate ester, may be obtained by the processing of certain vegetable and animal products containing fats.
The starting material for isolating, e.g., soy lecithin, is soy beans. Subsequent to cleaning, peeling and grinding the raw material, it is treated with solvents, and an oily product is obtained by extraction which contains lecithin in a colloidal solution. After additional treatment with water at elevated temperature and subsequent dehydration, the lecithin content of the solution is further enriched, whereby a semi-solid, pasty material is obtained, which is raw lecithin. It consists of approximately 60-70% phosphatides and approximately 30-40% oil components.
For the further processing and the technical utility of the lecithin, it is necessary to keep the oil component as low as possible. Since lecithins are used on a large scale in the production, processing and conservation of food items and also pharmaceutical and cosmetic preparations, exceedingly high requirements are established for the quality of the lecithins, in particular in relation to reservations as to physiological compatibility.
Heretofore, the oil content has been further reduced in costly purification processes, in part by boiling and evaporation or by means of further extraction with specific solvents and mixtures of solvents. These measures require either an additional subsequent, energy-intensive drying process, or else, in the case of the extration method, residual parts of the solvents which are used in a large excess remain in the lecithin, so that again the traces of foreign solvents must be removed. In these processes, the lecithin is exposed over extended periods of time to stressful conditions, such as, for example, elevated temperatures, whereby the danger of ester cleavages or other decomposition processes is enhanced.
The present invention concerns a new process for the production of pure lecithin which is directly usable for physiological purposes, wherein raw lecithin is treated with gas as the means for extraction under conditions which are supercritical with respect to pressure and temperature, in accordance with a specific series of process steps.
Extraction processes operating with supercritical gases as the means for extraction are known. Thus, according to the process of German Pat. No. 21 27 618, extracts of hops are produced by extraction with supercritical gases. But in this process, resinous components, ethereal oils and acid contents are equally removed in a non-selective manner.
According to the process of East German Pat. No. 41 362, substances as unlike in their polarity as silicone oil, paraffin oil and aluminum-sec-butylate may be extracted together and simultaneously with non-polar supercritical gases.
According to the process of German Offenlegungsschrift No. 27 09 033, camomile is extracted with a supercritical gas. In this process again, the extract will contain in addition to the extracts desired, large components of undesirable accompanying substances, such as, for example, lipoids, dyestuffs or pigments, etc. The content of these components may be produced by a special, costly procedure to a slight extent, without however being able to significantly reduce the content of lipoid components.